Friday, December 20, 2013

The Idea, the Design, the Mistake

I know, it's been a long time since my last post. But I was busy with other stuff and also my laziness (a skill which I have trained close to perfection) has prevent me from doing a new post.

This time I want to write about the good, the bad and the ugly the idea, the design and the mistake.

The Idea

While using an Arduino MEGA 2560 with the Ethernet shield I've discovered that there are still a lot of unused and free pins available.

It covers the pins 14-53 and A8-A15 (A6,A7 are also free but difficult to reach with a additional board).

These pins include:

USART 1-3 (14-19)

I2C (20,21)

PWM (44-46)

SPI (50-53)

ATmega2560 external memory interface (22-37, 39-41)

+5V and GND

This brought me to the idea to make a small prototyping shield for these pins.

The Design

For aesthetic reasons I wanted to make a *duino shaped board so I've downloaded the Arduino Mega 2560 reference design form the Arduino homepage to get the exact measurements for the pins and the board outline. Based on that I was able to create a EAGLE library with some templates (board outlines and connectors) to create own shields for the Arduino Mega.

The Mistake

After a lot of checks of the EAGLE *.brd file and additional checks of each of the Gerber layers I've ordered the the PCB at OSH Park. 24 Days later I've found the boards in a nice purple envelope in my mailbox.

I quickly unpacked the PCBs, fired up my soldering station and searched for some pin headers in my assortment boxes. Just some seconds after I have found the pin headers I have discovered that they do not fit trough the holes of the vias - I experienced a strong feeling of disappointment/frustration :-(

A cigarette later I decided to investigate what went wrong. I have discovered that the drilling of all vias in my design of the board where only 0.8mm and a diameter of at least 1.0mm is necessary to put pin header trough the holes. I've decided to make the holes of the vias for the connectors to the Arduino 1.2mm and the rest of the holes of the prototyping area 1.1mm.
I also have updated all packages in my EAGLE Arduino library

But even if the pin headers do not fit to the board I was able to see that it would fit nicely. So I have ordered the updated revision of the board directly again at OSH Park. In 3-4 weeks I will see the final result.